The present invention relates, in general, to ultrasonic imaging and, in particular, to a probe in which the scan plane of an ultrasonic transducer unit can be changed, so that a body organ, such as the heart, which is being imaged can be viewed in different ways (i.e. in longitudinal and transverse sections or any section inbetween). Such a probe often is referred to as a "multi-plane" probe by those skilled in the art. Many different ultrasonic multi-plane probes have been suggested or put into actual use in the past. Typically, in these probes, the ultrasonic transducer unit is positioned in a cavity in a housing with the cavity filled with a fluid and covered by a membrane. The ultrasonic probes described and illustrated in U.S. Pat. Nos. 4,543,960 and 4,930,515 are representative of such probes. The scan plane of the ultrasonic array in the probe in U.S. Pat. No. 4,543,960, for example, is changed by operating a cable and pulley mechanism.
There are at least four shortcomings with the prior art ultrasonic multi-plane probes know to applicant. One is size. Although, these probes are small to begin with, even smaller probes are highly desirable.
A second problem with the prior art ultrasonic multi-plane probes known to applicant is the very presence of the fluid in the cavity and the potential damage to the ultrasonic array caused by swelling or corrosion due to the presence of the fluid in the cavity. The fluid is provided in such probes to establish the proper acoustic coupling from the array into the membrane.
A third problem with the prior art ultrasonic multi-plane probes known to applicant is that the membrane cover, which is an added component in the acoustic path, can attenuate and distort sound waves in a manner which reduces ultrasound system resolution.
A fourth problem with such prior art ultrasonic multi-plane probes is that the positioning mechanism passes through sliding seals which are susceptible to leakage of body fluids into the probe cavity to contaminate the fluid in the probe cavity possibly leading to corrosion and acoustic problems. Leakage of the probe cavity fluid into the patient also can occur, but this is problem is overcome by using a biocompatible fluid in the probe cavity.